Process for the separation of isobutene from a mixture of c hydrocarbons



M; ONEM www1 G. B. ZIMMERMAN Filed Sept. 11. 1942 May 27, l947.

RROOEss ROR THE SEPARATION OF ISOBUTENE FROM A MIXTURE OF c4 HYDROCARBONS Patented May 27, ld?

PROCESS FOR THE SEPARATION 0F ISO- BUTENE FRQM A MIXTURE OF C4 HYDRO- CARBONS Gordon B. Zimmerman, Chicago, Ill., assigner to Universal Gil Products Company, Chicago, Ill.

a corporation of Delaware Application September 11, 1942, Serial No. 457,943

This invention relates to the separation of oleiinic hydrocarbons from paraiiinic hydrocarbons i claims. (oi. 26o- 677) and is more particularly concerned with the separation of isobutylene from mixtures of saturated and unsaturated C4 hydrocarbons.

The production of synthetic rubber has assumed considerable importance at the present time. Two of the most important methods of producing synthetic rubbers are the polymerization of isobutene and butadiene and the polymerization of styrene and butadiene. The physical properties of the synthetic rubbers produced by the above polymerization processes are dependent to a large extent upon the purity of the reacting hydrocarbons which controls the length of the chain of the hydrocarbons in the synthetic rubber polymer.

The present invention discloses a method for separating the isobutene from the various other C4. hydrocarbons and in conjunction with the separation process produces hydrocarbons suitable for further dehydrogenation to butadiene.

It is Well known that simple fractional distillation of a mixture of C4 parains and olens does not result in a practical separation since the boiling points of the various hydrocarbons are somewhat similar. This is particularly true with a mixture of C4 olens and parafns containing the isomers, as will be evident by studying the table presented below.

Boiling points at 1 atmosphere pressure It is evident from the above boiling points that a separation of the individual hydrocarbons by simple fractional distillation is practically impossible. It is also evident that it is comparatively easy to separate the C4 hydrocarbons into two fractions, the overhead containing isobutane, isobutene and normal butene-l and the bottoms containing normal butane, normal butene-Z trans and normal butene-Z cis. However, the separation of isobutene and normal butene-l is practically impossible by fractional distillation since the difference in the normal boiling point is approximately 0.2 of a degree F.

The present invention provides a simple efficient method of removing the normal butene-l hydrocarbon from the isobutane-isobutene fraction which may subsequently be separated into isobutane and isobutene. rIfhis method consists of isomerizing the normal butene-l to normal butene-Z either the trans orv cis form and removing this hydrocarbon by fractional distilla-` tion.

This isomerization may be effected by conBl tacting the C4 mixture following the separation of the normal butanes and butene-.Z with a number of catalysts under specific conditions of temperature, pressure yand Contact time. The primary feature of the present invention is the conductionY of the iscmerization reaction under processing conditions such that the isomerization of butene-l to butene-Z cis and trans forms occurs at such a rapid rate that the isomerization may be accomplished without any substantial effect on the isobutene in the C4 fraction charge. The particular set of conditions chosen will be dependent upon the type of catalyst being utilized since the catalyst will regulate the reaction rates of the various isomerization reactions.

The butane-butene fractions which can be effectively treated in the process of this invention may be the exit gases from a catalytic cracking operation, catalytic dehydrogenation operation, thermal cracking operation or similar hydrocarbon conversion processes which produce butane-butene fractions containing the Various.`

C4 hydrocarbons.

This invention is particularly useful in con-. junction with processes for the production of.,` butadiene either by the single stage catalytic2 dehydrogenation of normal butane or by the two.

stage catalytic dehydrogenation of normal bu, tane to butenes which are subsequently dehydrogenated to butadiene. The isobutene hydrocar Y bon which is formed during the reaction has been found to undergo decomposition to carbon and hydrogen and increase the carbon deposi-I tion on the catalyst to a marked extent. The elimination of the isobutene from the recycle to catalytic zone tends to decrease the regenerating requirement of the operation.

In one specific embodiment, the present invention comprises a process for the separation of isobutene from a mixture of Ci hydrocarbons con-` taining substantial amounts of isobutene and normal butene-l which comprises contacting the isobutene and normal butene-l mixture with an olefin isomerizing catalyst under processing conditions regulated to selectively isomerize the nor- 55 mal butene-l to normal butene-Z and subsequently separating the isobutene from the reaction products.

The process of this invention will be more fully explained in the description of the accompanying diagrammatic drawing which illustrates in conventional side elevation one type ofY apparatusin which the objectsoffthe invention may be accomplished.

For simplification, such equipment as con densers, coolers, furnaces, control valves and the like which are not essential tothe.expla nationr have been omitted from the drawing.l

Referring to the drawing a butane-butene mixture containing isobutene, isobutaneand butene l obtained by the preliminary separation of the. C4 hydrocarbons from any suitable source such as catalytic cracking, catalytic dehydrogenation or thermal cracking, is introduced through line4 l containing valve 2 into pump 3 which discharges,` through line 4 containing valve 5 into reactor `6 wherein the heated hydrocarbons are contacted withA a suitable4` isomerizing catalyst under con?" dudas such that, the huele- 1, inthe .C4 fraaie. is selectively isomerizedv tovbutene-Zl "The iso*-V butene andisobutanenin thCi fraction aresubY-n stantially unaiected under Vthe particular operati ing conditions chosen. N

rT hencatalyst Within reactor limmaycompriseaF synthetic composite of silica-alumina,Y silicaalu-f, minal-zirconia, activatedclays, aluminum sulfate, kieselguhr impregnatedA with phosphoric acid, bauxite, aluminumphosphate, pumice andW lime. Various other c atalystswsuchf` as liquid phosphoric acid, benzene sulfonic acid, perchloric acid vand aqueous zinc chloride may also be used. The solici catalysts recited abovezr'na'y be utilized in the granular'form disposedwithin reactor 6to form a fixed bed through which the C4 hydrocarbons will pass or they may be yutilized in powdered form. Utilization of a powdered catalyst is particularly eiective if operatedunder conditions suchthat a fluidized catalyst mass is obf tained,` the iluidizing medium being the heated`V C4 vapors.

|The ltemperature in isomerization zone E will be dependent primarily upon the type of catalyst usedb- When phosphoric acid` or other acidcatalysts which may also actas polymerizationcatalysts are used, the temperature will ordinarilyl be within the approximate range cfr-50 to 500 Under certain conditions some of the catalysts will tend to promote the polymerizatiomoffthe olens alongY with the.. isomerizationreaction. However, the isomerization. reaction isacompar.- atively easy reactionand proceeds at avery rapidl rate ,under the iniiuence of ,a catalyst. Theree. fore, bytheproperselection of therprocessingA conditions, the `polymerization..Will ,be held ata,

respect to any individualfcatalystwill'be .such

that the actual accelerating.Qithjiseeerizaiie valve,v I9 may be treated in a manner similarl to of butene-l to butene-2 is so much greater than the reaction rate of isobutene to butene-2 that the desired isomerization reaction can be accomplished without any substantial conversion of the isobutene.

Fromisomerization zone nthe reaction products Vcontaining isobutane, isobutene, y* butene-Z, unconverted butene-l and the small amount of polymer formed during the reaction are directed through line 1 containingr Valve 8 into fractionator` 9 wherein the Aisobutene, isobutane and unconverted butene-l are separated from the butene-2 and polymer. The isobutene, isobutane and unconverted butene-l are withdrawn through linei containingvalve Il and if no substantial amount ofbutene-l remains therein, are withdrawn through line 22 containing valve 23 and sent to a separation step wherein the isobutene is separated from the isobutane by any of the well known means known to those skilled in the 11151191.1 a-.S .SQlYent extcffn aZeOF-oldilt lation, selrendistillatien, elle 'leebilteherZ is Withdrawn through line *i2A contain'inngvalve i3A and maybe ,recoveredas a productuof the reaction or further processed, for example, to produce Y butadiene. The'polymer isv withdrfav/ riy through linemcontaining Valve 25g.;

It the C4 Vfraction withdrawn through line I0 contains a. substantial amount of unconverted buteneflnthefstream of'hydrocarbons` is directed into'reactorA I4 Vwhich is similar Yto reactor 6 further yisomerization of the butene-l Vaccomplished, TheY reaCtOn products from reactor I4- arewithdrawn through line I5 containing valve wand directed into fractionatorllwherein thel isobuteneisobutanev is separated from the bu-A tene-2 and polymer. The birrerie-ais withdraw@ through line 20`containing valve 2i and,combined with theibutenze-Z in line4 i2, The isobutaneris'robuteneV withdrawn through line I8 Vcontaining that pointed out previously to separate a substan., tiallyl pure insobutene. The polymer is Witliv drawn through line 25 containing valve 21 and` is recovered as a product of the reaction.

The isqmerization of the catene-1' to tutelle-24 is an equilibrium reaction and as the hydrocarbonsreachequilibrium under the particular conditions chosenin the isomerizing zone, only the equilibrium conversions canV beobtained. However, by removing the butene-2 hydrocarbons formed-fthe equilibrium is disturbed and further isomerization can be conducted in subsequent processing zones. By successive isomerization withintermediate separation of the butene-Zfan isobutaneisobutere fraction substantially free of.

buteiqiel isorbta'iried.V Although onlytwo isomf-A erizzationv zones are shown in the drawing pre'- sented kiherefii, "it should be understood that thev present invention is not limited in this respect,

but is broad to any number of isomerization zones necessary to accomplish the desired object ofthe intenties.-

I claim ,as my invention:

1.*Aprocess'Y for the separation of isobutene from a mixtureof C4 l'iyclrocarbonscontaining isobutenelandbutene-l which comprises contacting saidmixture with an olefin isomerizing catallyst under, isomerizing conditions regulated to selectivelyisomerize .the butene-l to butene-Z without effecting to any substantial extent isonfleriza-` tion of the isobutene contained therein, and Subj 56.5111811911 fraetifznatins the. gebeten@ from the resultingjisobutene-butenez mixture.y

f2``A proce-s's` for 'the separation of isobutene from a mixture of C4 hydrocarbons containing isobutene and butene-l which comprises contacting said mixture with a phosphoric acid catalyst under isomerizing conditions regulated to selectively isomerize the butene-l to butene-Z Without effecting to any substantial extent isomerization of the isobutene contained therein, and subsequently fractionating the isobutene from the reaction mixture.

3. A process for the separation of isobutene from a mixture of C4 hydrocarbons containing isobutene and butene-l which comprises contacting said mixture with a silica-alumina catalyst under isomerizing conditions regulated to selectively isomerize the butene-l to butene-2 Without effecting to any substantial extentl isomerization of the isobutene contained therein, and subsequently fractionating the isobutene from the reaction mixture.

4. A process for the separation of isobutene from a mixture of C4 hydrocarbons containing isobutene and butene-l which comprises selectively isomerizing the butene-l to butene-2 without effecting to any appreciable extent isomerization of the isobutene by contacting said mixture with a phosphoric acid catalyst at a temperature of from about 50 to about 500 F., at a liquid hourly space velocity of from about 3 to about 50 and subsequently fractionating the isobutene from the reaction mixture.

5. A process for the separation of isobutene from a mixture of C4 hydrocarbons containing isobutene and butene-l which comprises selectively isomerizing the butene-l to butene-2 Without, eiecting to any appreciable extent isomerization of the isobutene by contacting the hydrocarbon mixture with a silica-alumina catalyst at a temperature of from about 400 to about 1000 F., at a liquid hourly space velocity of from about 3 to about 50 and subsequently fractionating the isobutene from the reaction mixture.

6. A process for the separation of isobutene from a mixture of C4 hydrocarbons containing isobutene and butene-l which comprises contacting said mixture with an olen isomerizing catalyst under isomerizing conditions whereby the butene-l is selectively isomerized to butene-2 Without effecting to any substantial extent isomerization of the isobutene, fractionating the reaction products to separate the butene-2 from the isobutene and unconverted butene-l and introducing the isobutene and unconverted butene-l to a second isomerzation Zone to convert substantially all of the butene-l to butene-2, and subsequently fractionating the reaction products to separate isobutene substantially free from butene-l.

7. A process for the separation of isobutene from a mixture of C4 hydrocarbons containing isobutene and butene-l which comprises contacting said mixture with an aluminum sulfate catalyst under isomerizing conditions regulated to selectively isomerize the butene-l to butene-2 Without effecting to any substantial extent isomerization of the isobutene, and subsequently fractionating the isobutene from the reaction mixture.

GORDON B. ZIMMERMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENT Number Name Date 2,281,804 Ruthruii;` May 5, 1942 2,199,133 Marschner Apr. 30, 1940 2,298,931 Drennan Oct. 13, 1942 2,388,510 Voge Nov 6, 1945 2,330,115 Drennan Sept. 21, 1943 

